¨ This post-effective amendment
designates a new effective date for a previously filed post-effective amendment.

This filing relates solely to the following Fund, a series of iShares U.S. ETF Trust:

iShares Enhanced U.S. Small-Cap ETF

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, as amended, and the Investment Company Act of 1940, as amended, the Registrant certifies that it meets all the requirements for the
effectiveness of this Registration Statement pursuant to Rule 485(b) under the Securities Act of 1933, as amended, and has duly caused this Post-Effective Amendment No. 12 to the Registration Statement to be signed on its behalf by the undersigned,
duly authorized, in the City of San Francisco and the State of California on the 29th day of April, 2013.

iSHARES U.S. ETF TRUST

By:

Michael Latham*

President and Trustee

Date: April 29, 2013

Pursuant to the requirements of the Securities Act of 1933, as amended, this Post-Effective Amendment No. 12 to the
Registration Statement has been signed below by the following persons in the capacities and on the date indicated.